The amendment enacted Thursday consolidates military power under a new role, chief of defence forces, who commands Pakistan's army, navy and air force.

It also gives Munir lifelong immunity from criminal proceedings, potentially awarding him unchecked powers.

Munir became army chief in November 2022 after serving in senior positions including as quartermaster general and Corps Commander Gujranwala.

He was also head of the Military Intelligence and later of Pakistan's powerful spy agency Inter-Services Intelligence.

In 2019, he was removed as intelligence chief just eight months into his stint, under then-prime minister Imran Khan and for reasons that have never been made public.

Munir's fortunes changed after lawmakers ousted Khan. The ensuing Shehbaz Sharif government gave him charge of the military.

In May this year, following a four-day clash with India, Munir was promoted to field marshal.

"We achieved a historic victory," Law Minister Azam Nazeer Tarar told parliament this week, saying "everyone appreciated General Asim Munir" for it.

"India challenged our territorial sovereignty. The whole nation supported the armed forces and the government at that time," he said.

But Aqil Shah, author and professor at Georgetown University, said the conflict "was dominated by air combat, not land-based operations" which are typically associated with field marshal honours.

- 'Most powerful man' -

"This is a case of 'autocratic legalism'," Shah told AFP. "In no other democracy is the army chief of staff the designated joint service chief."

Shah said that the change granting Munir immunity from prosecution "makes redundant Article 6 of the constitution, which criminalises military coups".

AFP has contacted a spokesman for the Pakistani military for comment.

"Field Marshal Asim Munir has become the most powerful man in Pakistan," said defence analyst Naeem Khalid Lodhi, a retired lieutenant general.

"The politicians are responsible for making him even more powerful. For their short-term interests, they have put Pakistan's long-term interests at stake," he told AFP.

A coalition of parties considered pliable to the powerful military formed a government after Pakistan's February 2024 elections, in which Khan -- the nation's most popular politician -- was jailed and barred from running.

Shuja Nawaz, an author and expert on South Asia, sees the amendment vote as a survival strategy.

Politicians "renewed their insurance policy," he said.

"Munir's five-year term will outlast theirs, and they expect his support when elections come."

To Lodhi, "the constitution governs the affairs of the state, and only a genuinely representative government can amend it."

- Need for stability -

Nawaz said Munir now "probably has as much power" as the late military ruler Pervez Musharraf, who seized power in 1999.

"Like Musharraf, he has a subservient prime minister and the authority to reshape the army's structure," he said.

Nawaz noted that Munir, in his new role as chief of defence forces, can also overhaul military command and "modernise the force".

The lifetime rank was not unusual and follows British tradition, Nawaz added.

"Field marshals don't retire. They may leave a post, but they remain field marshal for life," he said.

Munir has already scored some diplomatic wins, including a private lunch with US President Donald Trump.

But, Nawaz warned, "Trump is unpredictable, and India remains a bigger draw for Washington.

"Pakistan's future lies in a strong economy and stable political system -- neither of which it has right now."